1. Field of the Invention
The present invention relates to a method and apparatus for estimating the condition of a road surface on which a vehicle is traveling and a method for vehicle control.
2. Description of the Related Art
For improved travel stability of a vehicle, it is desired that the coefficient of friction between the tire and the road surface (surface friction coefficient) or the ground contact state of the tire is estimated accurately and the data thus obtained is fed back to vehicle control. If the surface friction coefficient or the ground contact state of the tire can be estimated in time, then it will be possible to operate such advanced control as ABS (antilock braking system) braking before any danger avoidance action, like braking, accelerating, or steering, is taken. With such facility, there will be a marked boost in the safety of vehicular operation.
In a method for estimating a surface friction coefficient, such as one disclosed in Japanese Unexamined Patent Application Publication No. 2010-274906, a tire used for the estimation of a road surface condition has deformable structural areas including sipes formed at a specific pitch P circumferentially in the shoulder region. And a vibration spectrum is acquired by detecting the vibrations of the tread of the moving tire by an acceleration sensor. At the same time, a detection frequency is calculated from the wheel speed measured by a wheel speed sensor and the pitch P. Then a road surface condition is estimated, using the amplitude of the vibration level caused by the deformable structural areas at the detection frequency.
However, a problem with the above-described conventional tire for estimation of a road surface condition is its well-defined tread pattern which restricts the freedom of tread pattern design.
The present invention has been made to solve the above-described problems, and an object thereof is to provide a method and apparatus for accurately estimating the condition of a road surface on which a vehicle is traveling, and a vehicle control method, using a tire having a common variable-pitch tire pattern for detection of a road surface condition.